Pressure sealed belt filter systems are used to remove solid contaminants from a liquid. Filtration systems which automatically sequence in cutting off liquid inflow, the removal of accumulated solids from the filter media and the replacement of the filter media with a new media are known. Filtration apparatus for use in such systems are shown in U.S. Pat. No. 2,867,326, assigned to the assignee of the present invention. In the apparatus therein disclosed, fluid conducting shells are provided that are capable of sealing a filter medium therebetween. One of the filter shells is movably mounted and actuated by a fluid pressure cylinder to its sealing position. The disadvantage of such an apparatus is the limitation of operating pressure to the resisting capacity of the shell motivating mechanism.
U.S. Pat. No. 3,333,693, also assigned to the assignee of the present invention, discloses a filter apparatus where a movable seal frame is utilized. Two fixed filter shells adequately reinforced by a rigid structure are provided. The seal frame is utilized to confine the filter medium against one of the filter shells. The seal frame is held in position by the actuation of a fluid pressure cylinder. The design is limited to operation at pressures that are within the limit of the structural security of the seal frame and the actuation cylinder.